1. 1
   A cyclist's bicycle dynamo generates electricity to power the bicycle's front lamp. Inside the dynamo, a magnet spins near a coil of wire, which is connected in a complete circuit to the lamp.

   (a)

   What is the correct term for the effect that produces a current in the coil as the magnet spins?

   [1 mark]

   • AThe generator effect
   • BThe motor effect
   • CElectrostatic induction
   • DNuclear induction

   (b)

   The cyclist pedals faster, spinning the magnet inside the dynamo more quickly, but does not change anything else about the dynamo. What happens to the potential difference induced across the coil?

   [1 mark]

   • AIt drops to zero
   • BIt decreases
   • CIt stays exactly the same
   • DIt increases

   (c)

   Give two ways, other than spinning the magnet faster, that the dynamo could be redesigned to increase the size of the potential difference induced in the coil.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A wind turbine at a coastal wind farm uses the generator effect to produce electricity for the National Grid. Inside the turbine, the spinning blades turn a coil of wire within a strong magnetic field.

   (a)

   Which statement correctly describes the type of electrical supply produced by this type of generator (an alternator)?

   [1 mark]

   • AA constant potential difference, because the magnet does not move
   • BA direct current, because the coil is only moving in one direction
   • CAn alternating current, because the direction of the induced current reverses as the coil rotates
   • DNo current at all, because the coil is inside a sealed casing

   (b)

   During a storm, the wind speed doubles and the turbine blades spin at twice their previous rate, with no other changes made. What effect does this have on the frequency of the alternating potential difference generated?

   [1 mark]

   • AThe frequency halves
   • BThe frequency doubles
   • CThe frequency stays the same
   • DThe frequency becomes zero

   (c)

   State the law that describes the direction of an induced current, and explain what this means for the direction of the induced current in the turbine's coil in terms of the magnetic field it creates.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A moving-coil microphone, used by a singer during a live concert, contains a coil of wire attached to a thin diaphragm, placed within the magnetic field of a small permanent magnet.

   (a)

   Explain how sound waves reaching the microphone's diaphragm result in a varying electrical current being produced in the coil.

   [3 marks]

   (b)

   The sound engineer notices that quieter sounds produce a smaller electrical signal from the microphone than louder sounds. Explain, in terms of the diaphragm's movement, why louder sounds produce a larger induced potential difference.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital emergency generator uses a petrol engine to spin a coil of wire within a magnetic field, producing an alternating potential difference to power essential equipment during a power cut.

   (a)

   Explain how this generator produces an alternating potential difference as the coil rotates through one complete turn, and explain why the potential difference is greatest at particular points in the rotation and momentarily zero at others.

   [6 marks]

   (b)

   The hospital engineer is deciding whether to upgrade the emergency generator so that it produces a higher potential difference without changing the engine's rotation speed. Explain, using ideas about the generator effect, two separate design changes that could be made to the generator to achieve this, and explain why each change would have this effect.

   [6 marks]

   Total for question 4: 12 marks

End of questions